1. Field of the Invention
This invention relates to an exhaust gas analysis system for determining the concentration of selected contaminants in the exhaust gas emission from a motor vehicle, and particularly to an exhaust gas analysis system which is compensated for changes in ambient pressure and exhaust gas temperature. The concentration of specified components in the vehicle exhaust gas, such as CO and HC is measured by a nondispersive infrared gas analyzer whose output is automatically compensated, by either digital or analog techniques, to take into account changes in ambient pressure and changes in the temperature of the exhaust gas.
2. Description of the Prior Art
Becaue of the recent public concern with environmental pollution, particularly that caused by the contaminants in the exhaust gas from motor vehicles, a number of exhaust gas analysis systems have been developed to determine the concentration of the exhaust gas contaminants. Because of their inherent accuracy and reliability, many governmental agencies have specified that vehicle exhaust gas analysis systems contain nondispersive infrared gas analyzers as the component in the system which measures the concentration of the contaminants in the exhaust gas. However, such gas analyzer units are normally calibrated only by the manufacturer and do not take into account changes in ambient pressure at the location where the exhaust gas analysis takes place, or changes in the temperature of the exhaust gas from the vehicle under analysis.